1. Field of the Invention
The invention relates to a technique of identifying which of an electrically-driven hydraulic pump and a solenoid valve is malfunctioning when an abnormality of the power transmitting state is detected, without increasing the number of components.
2. Description of Related Art
There is known a vehicle including a torque converter, a hydraulic clutch, a mechanically-driven hydraulic pump, an electrically-driven hydraulic pump, and a solenoid valve. The torque converter is disposed between an engine and an automatic transmission. The hydraulic clutch is disposed in the automatic transmission. The mechanically-driven hydraulic pump is driven by the engine. The electrically-driven hydraulic pump is driven electrically. The solenoid valve controls the operation of the hydraulic clutch using the discharge pressures from the mechanically-driven hydraulic pump and the electrically-driven hydraulic pump as source pressures, or using the discharge pressure from the mechanically-driven hydraulic pump as a source pressure. There is also known a technique of automatically stopping an engine when a vehicle stops travelling, and starting the engine using a starter in response to a starting operation, thereby enabling the vehicle to start travelling. Further, there has been proposed provision of an abnormality determining apparatus that determines whether or not there is an abnormality in the power transmitting state due to a malfunction of a hydraulic circuit of the vehicle. An example of such an abnormality determining apparatus for a vehicle hydraulic circuit is described in Japanese Patent Application Publication No. 2002-115579 (JP 2002-115579 A).
The abnormality determining apparatus for a vehicle hydraulic circuit in JP 2002-115579 A includes transmitting state determining means and output limiting means. When an engine is started in a state where power is transmittable from the input side to the output side of an automatic transmission due to the discharge pressure from an actuated electrically-driven hydraulic pump, the transmitting state determining means determines whether the power transmitting state such as the operation controlled state of a hydraulic clutch is normal or abnormal based on, for example, the difference between the turbine speed of a torque converter (input rotational speed) and the output rotational speed of the automatic transmission. When the transmitting state determining means determines that the power transmitting state is abnormal, the output limiting means decreases the engine output torque or limits an increase in the engine output torque. This reduces occurrence of a shock due to an abrupt power transmission at the time of actuation of the mechanically-driven hydraulic pump in the case where the power transmitting state is determined to be abnormal.
Possible causes of an abnormality in a vehicle hydraulic circuit include a malfunction of a solenoid valve that adjusts the engagement pressure to be supplied to a hydraulic clutch (starting clutch), and a malfunction of an electrically-driven hydraulic pump that serves as a hydraulic pressure source of the hydraulic fluid pressure to be supplied to the solenoid valve. However, the abnormality determining apparatus for a vehicle hydraulic circuit in JP 2002-115579 A includes the means for determining whether or not there is an abnormality in the power transmitting state, but does not include any means for identifying a malfunctioning component that is a cause of the abnormality.
Therefore, hydraulic pressure detection sensors that detect actual hydraulic pressures may be provided downstream of the electrically-driven hydraulic pump and the solenoid valve. Then, which of the electrically-driven hydraulic pump and the solenoid valve is malfunctioning may be identified by measuring the discharge pressure from the electrically-driven hydraulic pump and the supply pressure to be supplied from the solenoid valve to the hydraulic clutch. However, providing such hydraulic pressure detection sensors increases the number of components, resulting in an increase in the production cost.